Wendigo

Ambusher. In the first round of a combat, the wendigo has advantage on attack rolls against any creature it surprised.

Flesh Eater. If the wendigo hits an incapacitated humanoid with a bite attack, the attack is automatically a critical hit.

Mimicry. The wendigo can mimic any sounds it has heard, including voices. A creature that hears the sounds can tell they are imitations with a successful DC 14 Wisdom (Insight) check.

Keen Smell. The wendigo has advantage on Wisdom (Perception) checks that rely on smell.

Regeneration. The wendigo regains 10 hit points at the start of its turn. If the wendigo takes fire damage, this trait doesn't function at the start of the wendigo’s next turn. The wendigo dies only if it starts its turn with 0 hit points and doesn't regenerate.

Sight Based Movement. A creature that has not moved on its turn can attempt to hide from the wendigo even if it is unobscured and within the range of the wendigo’s blindsight.

Spider Climb. The wendigo can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Multiattack. The wendigo makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 15 (2d10 + 4) piercing damage.

Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) slashing damage. If the target is Large or smaller, the Wendigo can choose to grapple it on a hit instead of dealing damage.

Rampage. When the wendigo reduces a creature to 0 hit points with a melee attack on its turn, the wendigo can take a bonus action to make a bite attack against the creature and then move up to half its speed.